1. Field of the Invention
The present invention relates to methods for forming a polycrystalline silicon film to improve electron and hole movement by doping with impurities.
2. Description of Related Art
Polycrystalline silicon is widely used as a material such as for thin film transistors (TFT) in semiconductor devices. Decompression chemical vapor deposition (CVD) utilizing monosilane (SiH4) as the gas is the generally used method for forming a film of polycrystalline silicon.
However, in the polycrystalline silicon film formed by methods such as decompression chemical vapor deposition (CVD), the level of movement of electrons and holes within the film is low so that their use as is, such as for channels is difficult. Therefore, processes such as laser annealing (ELA) or heat treating of the film after forming, are performed to improve the extent of hole and electron movement within the film.
However, even if these heat treating or laser annealing processes are performed on a polycrystalline silicon of the conventional art, the extent of movement is limited to about 80 to 120 cm2/Vxc2x7sec. The fabrication of further high performance semiconductor devices is therefore difficult to achieve.
Further, if a catalyst CVD method is utilized instead of the decompression CVD method, a polycrystalline silicon film with a movement level up to 50 cm2/Vxc2x7sec can be obtained without annealing. However, even if annealing is performed on the this polycrystalline silicon film, the extent of movement obtained will be drastically low compared with electron movement of approximately 540 cm2/Vxc2x7sec in a single crystalline film so that the movement level is still to low for fabricating a high performance semiconductor device.
In view of the above described problems with the conventional art, it is therefore an object of the present invention to provide a method for forming a polycrystalline silicon film to improve electron and hole movement and thus allow the fabrication of high performance semiconductor devices.
In order to achieve the above objects of the invention and solve the above problems of the related art, according to one aspect of the present invention, there is provided a polycrystalline silicon film forming method utilizing as a basic material, a chemical compound comprising at least one type of impurity from among tin (Sn), germanium (Ge) and lead (Pb); and forming a polycrystalline silicon film doped with impurities from at least one type from among tin (Sn), germanium (Ge) and lead (Pb).
To also achieve the objects and solve the problems of the related art, according to another aspect of the present invention, after forming of the polycrystalline silicon film, a polysilicon film doped with impurities comprising at least one type from among tin (Sn) germanium (Ge) or lead (Pb) is formed.
In these forming methods, a polysilicon crystalline film is formed by doping with impurities of at least one type from among tin (Sn), germanium (Ge) and lead (Pb) in group N of the periodic table of the elements so that the polysilicon crystalline film obtained by adding these tin (Sn), germanium (Ge) and lead (Pb) is electrically inert from flaws in those crystals and also, the level of electron and hole movement is increased due to the crystalline disarray and to internal stress.